Impact test method and application of impact tester

The test for measuring the impact resistance of metal materials is also called the impact toughness test. It is one of the basic test methods for testing the mechanical properties of materials. In an impact test, the energy consumed to break a sample is called the impact work and the unit is Joules (J), which is represented by Ak. Dividing Ak by the cross-sectional area F at the notch of the sample yields Ak/F=ak, and the unit is Joules/cm 2 (J/cm 2 ), which is called the material impact value. Ak can be used to assess the degree of material toughness and brittleness, but it cannot be directly used for design calculations.

According to the sample shape and breaking method, the impact testing machine can be divided into three kinds of bending impact testing machine, torsional impact testing machine and tensile impact testing machine. Among them, the pendulum bending impact tester is the most widely used, and the method is the most simple. The result of the impact test of the impact test specimen is closely related to the shape of the specimen. Test results obtained with specimens of different sizes and shapes cannot be compared with each other. Therefore, all countries are required to have standard samples. The Chinese standard mainly adopts the Mei-style sample and the Charpy V-notch specimen for the impact test to be very sensitive to the defects of the metal material, and can detect the defects and the organizational changes of the material during the smelting and processing processes. When the same sample is subjected to an impact test at a high to low temperature, the impact work (or impact toughness) will change from large to small, the number of crystalline fractures will increase from small to large, and the plastic deformation will vary from large to small, indicating that the material is in a tough state. Transition to the brittle state, usually the temperature at which the 50% crystalline fracture surface appears on the fracture is called the ductile-brittle transition temperature or brittle transition temperature.

Cobalt, elemental symbol Co, silvery white ferromagnetic metal, slightly silvery white on surface, 4th period in Periodic Table, Group VIII, atomic number 27, atomic weight 58.9332, hexagonal close packed, common valence of +2 , +3. Cobalt is a shiny steel gray metal, relatively hard and brittle, ferromagnetic, magnetic disappeared when heated to 1150 ℃. Cobalt has valences of +2 and +3. It does not interact with water at room temperature and is stable in humid air. Cooled to CoO when heated in air to above 300 ° C, and burned into Co3O4 when whitened. Hydrogen reduction method made of fine metallic cobalt powder in the air can spontaneous combustion of cobalt oxide. Cobalt is an important raw material for the production of heat-resistant alloys, hard alloys, anti-corrosion alloys, magnetic alloys and various cobalt salts.

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